Windows XP SP3

Windows XP Service Pack 3 (SP3) contains major security improvements designed to provide better protection against hackers, viruses, and worms. Windows XP SP3 also improves the manageability of the security features in Windows XP and provides more and better information to help users make decisions that may potentially affect their security and privacy. Microsoft strongly urges customers with Windows XP and Windows XP Service Pack 1-based systems to update to Windows XP SP3 as soon as possible.

From Microsoft:

Virus and Malware Tests: For security reasons, you should also check out the Windows XP SP3 download at LO4D.com which includes virus and malware tests. Additional screenshots of this application download may be available, too.